This invention relates in general to a mechanism for damping tape vibrations in a magnetic tape recorder and, in particular, for magnetic tape recorders of the type which record binary data.
One of the directions in the development of magnetic tape recorders which are used to store digital data has lead to higher and higher tape speeds. Magnetic tape recorders having a nominal tape speed of 200 inches per second (ips), corresponding to about 5 m per second, are already currently available in the marketplace. Binary data are written in formated blocks and commercially available magnetic tape recorders use an interblock gap of about 7 mm for reasons of storage capacity. In start/stop operation, this corresponds to the path within which the magnetic tape recorder must be stopped and restarted. In magnetic tape recorder devices having high tape speeds, extremely high accelerations or retardations occur during the start/stop operation.
The forces acting on the data carrier, that is the magnetic tape, in start or stop phases cause tape motions or deformations in the region of the magnetic head of the tape recorder which are not entirely explained in detail. Included among the reasons for this is that the forces in magnetic tapes of variously manufacturers act differently even when used in the same magnetic tape recorder.
Apparently, the accelerating forces effect more or less pronounced local deformations of the magnetic tape even in the region of the head mirror of the magnetic head, these forces reduce the amplitude of the read output signal. In one type of magnetic tape, it is particularly the edge tracks which are affected by these forces of another type of magnetic tape are also affected by these forces of another type of magnetic tape.
Added to these problems is yet another influence which results from a feature of high performance magnetic tape recorders. In commercial magnetic tape recorders, the magnetic tape is transported from a take-off reel to a take-up reel for writing. Frequently, the tape transport ensues on the basis of a single capstan which can be reversed in moving direction and which is arranged adjacent to the magnetic head. Commercial magnetic tape recorders are frequently equipped such that they allow a reading even during a return transport of the magnetic tape from the take-up reel to the take-off reel, this function being usually referred to as "backwards read". During tape transport in the forward direction, the capstan is arranged following the magnetic head in the running direction of the magnetic tape and pulls the magnetic tape over the head mirror of the magnetic head. By contrast, when the tape is run in the opposite direction, the capstan pushes the magnetic tape over the head mirror.
This fact has differing consequences especially during the start or stop phases upon operation of the magnetic tape recorder for the functions of reading in the forward direction, as well as, in the reverse direction, since it is precisely during these phases that the buffered tape length in the buffer chamber of the magnetic tape recorder changes. Investigations have confirmed that the starting phase in conjunction with the device function "backwards read" is an especially critical operating condition. Particularly here, such glitches in the curve of the amplitude of the read output signals can occur and they may lead to read output errors even though commercial tape recorders can still clearly discriminate read output signals despite great fluctuations from the rated amplitude.
It can be concluded from the comparison of different amplitudes of read output signals during a tape transport in forward or reverse directions and during the starting phase of the magnetic tape recorder, that a different tape tension is one of the critical influencing variables. One could therefore attempt to eliminate the described problem by an increased tape tension. With a given tape run, that is, the geometrical fashioning of the tape drive, an increase in the tape tension via an increase of the pressurization in the buffer chambers leads to modifications of the properties of the tape drive in and of itself.
Narrow limits are therefore placed on an increase of the tape tension for avoiding other, undesired reactions on the tape transport, because the tape tension of 3.6 N prescribed by the standard may not be exceeded. An increase in the tape tension also has the disadvantages of a considerably increasing power consumption and, over and above this, an increase in the surface pressure between the magnetic tape and the magnetic head mirror also occurs. An increase in the tape tension alone is therefore not suitable for resolving the above described problem.
It is also known in the technology of magnetic tape recorders that a pressure pad may be utilized to improve the contact between the magnetic tape and the magnetic head mirror. In particular, this measure is known in conjunction with magnetic tape recorders of entertainment electronics or magnetic tape recorders of the lower performance category having lower tape speeds. Such a measure may still be justifiable in such devices, but its employment in fast running, commercial tape recorders is inapplicable because of an excessive tape wear. The pressure pad is also a disadvantage in that it causes excessive heating of the magnetic tape.
In order to overcome these disadvantages in the prior art and to avoid a local lift-off of the magnetic tape from the magnetic head mirror, a planar compressed air cushion could be generated opposite the head mirror in a pneumatic way as an equivalent measure of a mechanical element, such as a pressure pad, for pressing the magnetic tape against the head mirror. However, investigations have shown that no effective allevation for the disturbances in the amplitude of the read output signals can be achieved with a planar air pillow.